Binding Properties of a Monoclonal Antibody Directed toward Lead−Chelate Complexes

Abstract

A monoclonal antibody (2C12) that recognizes a Pb(II)−cyclohexyldiethylenetriamine pentaacetic acid complex was produced by the injection of BALB/c mice with a Pb(II)−chelate complex covalently coupled to a carrier protein. The ability of purified antibody to interact with a variety of metal-free chelators and metal−chelate complexes was assessed by measuring equilibrium dissociation constants. The antibody bound to metal-free trans-cyclohexyldiethylenetriamine pentaacetic acid (CHXDTPA) with an equilibrium dissociation constant of 2.3 × 10-7 M. Addition of Pb(II) increased the affinity of the antibody for the complex by 25-fold; Pb(II) was the only metal cation (of 15 different di-, tri-, and hexavalent metals tested) that increased the affinity of the antibody for CHXDTPA. The increased affinity was due primarily to an increase in the association rate constant. The antibody also had the ability to interact with ethylenediamine tetraacetic acid (EDTA), diethylenetriamine pentaacetic acid (DTPA), and structurally related derivatives, but with affinities from 50- to 10000-fold less than that determined for CHXDTPA. Addition of metals to EDTA-based chelators reduced the affinity of the antibody for these ligands. However, when DTPA was used as the chelator, addition of Pb(II) increased the affinity of the antibody for the complex by 200-fold. The sensitivity of prototype immunoassays for Pb(II) could be modulated by changing the structure of the immobilized metal−chelate complex and/or the soluble chelator used to complex Pb(II) in the test solution.